Electroacoustic system
An electro-acoustic system , also known as an electrical loudspeaker system ( ELA ), colloquially also known as an announcement system, is a public address system and essentially serves to pass on information, especially language. The systems used are therefore optimized for intelligibility and range and less for authenticity in the sound, as is the case with PA systems , which, unlike electroacoustic systems, are mainly used for live and concert sound . In terms of sound quality, however, modern PA systems definitely come into the area of PA systems.
Areas of application and properties
Electroacoustic systems are used in airports, train stations, public buildings, department stores and sports facilities. In the past, electroacoustic systems have been widely used in so-called local call systems.
In the GDR it was customary until the end of the 1980s to equip companies and other non-public institutions with a high number of employees with ELA. The systems were designated as commercial radio and must not be confused with commercial radio in today's sense.
The spectrum of applications of an ELA ranges from background music to the pause gong to notification of malfunctions and emergencies.
For this purpose, these systems are particularly fail-safe (electro-acoustic emergency warning systems / electro-acoustic emergency systems). For this purpose, redundant amplifiers, so-called emergency amplifiers, can be installed which, if a regular amplifier fails, are automatically looped in in its place with the help of pilot tone monitoring . Furthermore, if the system has to be operational in the event of a power failure, it is equipped with an emergency power supply or an uninterruptible power supply (UPS). To further increase operational reliability, impedance monitors can be used for the individual loudspeaker circuits, which can signal a change in the alternating current resistance, as occurs when loudspeakers are disconnected or if cables are damaged.
In practice, several loudspeaker circuits are usually set up. On the one hand, this enables targeted announcements in certain parts of the building, for example at stations for the individual platforms; on the other hand, this is a prerequisite for being able to distribute the required total output power of the system to several, then smaller-sized amplifiers, which in turn benefits the operational reliability of the system.
In contrast to PA systems, ELA systems can usually be operated by laypeople without any technical background knowledge. The devices for announcements and, for example, music playback have only a few setting options such as volume and on / off. Further operating elements, for which expertise is necessary, are hidden behind a flap or housed in lockable cabinets or rooms.
functionality
Electroacoustic systems always have only one sound channel, so they work in mono . The one or more microphone units , or other source of sound originating audio signals are generally with an absolute level of 0 dB (reference value U 0 = 0.7746 volts) in a symmetrical shape at the inputs of ELA on.
Control inputs for signaling (e.g. break gong) and alarming (e.g. fire alarm) can also be provided. The sound signals for this are generated by appropriate assemblies within the ELA and fed to the power amplifiers via a switching device in analogy to the speech and, if necessary, music signals.
Modern ELA transmit the audio signal digitally via communication networks (LAN, WAN, ...), whereby the speech is digitized directly at the intercom and is only converted back into analog signals before the amplifier . In between, for example, the data can be digitally processed to reduce the tendency to feedback .
100 volt technology
The outputs are designed in so-called 100-volt technology. The output voltage of the amplifier is stepped up to 100 volts at maximum power by means of a transformer , so that it can be transmitted over relatively thin cables and large distances without significant loss. It is also advantageous that a large number of loudspeakers can easily be grouped in parallel to one amplifier output. Every single speaker features a transformer (transformer), who stepped down to 100 volts back to the voltage for low systems. In a system, you only need to add the respective extraction rates of the individual loudspeakers. For example, twenty speakers of six watts (20 × 6 = 120) or twenty speakers of three watts and six speakers of ten watts (20 × 3 + 6 × 10 = 120) can be connected to an amplifier with an output power of 120 watts. Simple shielded wire lines of type JY (St) Y 2x0.8 are used as cables.
Commercial radio in the GDR
Up until the end of the GDR, it was common practice to equip companies and other facilities with large numbers of employees with so-called company radio. Its functionality essentially corresponded to the ELA that is still in use today and was based on i. d. Usually also on the 100-volt technology. In this respect, the term operating radio is a bit misleading, because the transmission was wired and not by radio. The name is more derived from a radio program intended for the company .
The company radio usually allowed two modes of operation: optional and compulsory program. The reception of the optional program could be influenced by the user, that of the compulsory program not.
The election program served i. d. R. of entertainment and general information for employees. For this purpose, broadcasts of the public radio were often fed into the commercial radio. In larger companies there were also their own recording studios with professional studio technology and z. Sometimes part-time or full-time editors who designed the broadcasts of the company radio and primarily devoted themselves to internal issues. The company radio often supplemented the information and service functions of the company newspapers . Usually there was a mixed operation, so that the commercial radio broadcast a public radio program for most of the time and only at certain times, e.g. B. in the breaks, sent own contributions.
The compulsory program was i. d. Usually only from announcements that should be accessible to all employees, e.g. B. Broadcasts, alerts and emergency announcements. Its reception could not be influenced by the users. The word refers to the so-called mandatory connection within the ELA and not to any obligation on the part of employees to listen to the program. While a mandatory program was being broadcast, the optional program was automatically muted.
Offices, break rooms, corridors and workshops were equipped with loudspeakers for reception of the company radio. In some companies, loudspeakers were also installed in the outdoor facilities. The loudspeakers in offices, break rooms and other smaller rooms had a volume control, with the help of which the volume of the choice program could be regulated or the choice program could also be turned off. The controller had no influence on the volume of the compulsory program. Loudspeakers where reception of the optional program did not make sense (e.g. in rooms with poor acoustic conditions, factory halls, outdoor facilities) were often only designed for receiving the mandatory program and were therefore out of order for most of the time.
For the transmission of the company radio programs i. d. Usually three or more core cables are used. One wire each served for the supply of the elective and the compulsory program and one wire as a common return line. A program wire in the loudspeakers was then connected via the volume control and a wire directly to the transformer.
Special industrial radio amplifiers with 100-volt technology were often used as amplifiers. In larger companies, remote sub-amplifiers were often operated in order to save line capacities. These amplifiers received the program via a 100-volt line - so they were connected to another amplifier like a loudspeaker. A switchover of the amplifier outputs could be effected via a remote switching criterion. In this way the distinction between elective and compulsory programs was realized.
literature
- Wolfgang Ahnert u. Anselm Goertz: PA technology. In: Stefan Weinzierl (Ed.): Manual of audio technology. Springer Verlag, Berlin, 2008, ISBN 978-3-540-34300-4
- Siegfried Wirsum: Practical sound reinforcement technology. Device concepts, installation, optimization. Franzis-Verlag GmbH, Munich 1991, ISBN 3-7723-5862-4 .
- R. Beckmann: Manual of PA technology, basic component practice. 2nd edition, Elektor-Verlag, Aachen, 1990, ISBN 3-921608-66-X
Web links
- Baunetz knowledge: Electroacoustic systems (ELA) for emergency alarms
- Advantages of 100-volt technology - pdf (99 kB)